This invention relates, in general, to a metallization scheme providing adhesion and barrier properties, and more particularly, to a packaging interconnect metallization scheme used in semiconductor device manufacture to provide electrical contact to a semiconductor substrate.
Barrier and adhesion metals used in semiconductor device manufacture can be used as part of a packaging interconnect metallization. A chip level interconnect metallization makes electrical contact to the semiconductor chip, while the packaging interconnect metallization provides the electrical contact between the chip level interconnect metallization and a wire or a conductive lead.
Several methods may be used to package a semiconductor die or chip. Standard die attach and wire bonding techniques or Tape Automated Bonding (TAB) are two such methods. In conventional wire bonding a barrier and adhesion metallization scheme may be provided between the chip level interconnect metallization and a conductive metal pad. A wire may then be bonded to the conductive metal and the package. In TAB, a barrier and adhesion metallization scheme is provided between the chip level interconnect metallization and a bump metallization. The bump metallization provides an interface between the semiconductor chip and a conductive lead on the tape. The barrier and adhesion metallization scheme must provide good adhesion to the chip level interconnect metallization, the chip dielectric or passivation layer, and the bump metallization. The metallization must also exhibit good adhesion properties when subjected to high temperatures. After packaging, a semiconductor die may see temperatures of as high as approximately 400.degree. C., therefore, the adhesion of the metallization must be able to withstand these temperatures. It is especially important that the adhesion is reliable in the packaging interconnect metallization because it must be able to pass wire pull or lead pull tests. The barrier and adhesion metallization scheme must also provide a barrier to the diffusion of other metal atoms through it. The diffusion of other metal atoms must by prevented because an unfavorable reaction between some metals may occur, causing corrosion and eventual reliability problems. In addition, the diffusion of some metals to the semiconductor substrate may cause a degradation in the electrical characteristics of the device.
Many different metallization schemes are used to provide barrier and adhesion properties. Titanium-tungsten (TiW) is a well known barrier and adhesion layer. Meyer et al discuss the use of a TiW/Au metallization scheme layer in a paper entitled, "Metallurgy of TiW/Au/Cu System for TAB Assembly," published in J. Vac. Sci. Technol., May/Jun '85, pp. 772-776. In this reference the chip level interconnect metallization is aluminum and the bump metallization is gold. The passivation layers used were heavily doped PSG, silicon nitride, and polyimide The TiW acts as both the adhesion and barrier layers. The conductive leads of the tape are made of copper.
Although Meyer et al discuss that improvements in the barrier properties of TiW can be achieved by sputtering the TiW in the presence of nitrogen to form a titanium-tungsten-nitride (TiWN), no attempt was made to use TiWN. TiWN has been shown to have improved barrier properties over TiW in a paper by Nowicki et al entitled, "Studies of the Ti-W/Au Metallization on Aluminum," published in Thin Solid Films, Vol. 53, 1978, pp. 195-205. The use of a TiW/TiWN/TiW/Au metallization is discussed. The interdiffusion between aluminum and gold with the TiW/TiWN/TiW as the barrier and adhesion metallization scheme is discussed Here the two layers of TiW act as adhesion layers to the aluminum layer and the gold layer. TiWN acts only as a barrier layer. Nowicki et al do not suggest that TiWN may be used as an adhesion layer. The TiWN is sandwiched between the TiW layers because the TiWN has different adhesion properties than TiW. Thus, even though the TiWN has been proven to improve the barrier properties, in the past, TiWN has not been thought to be entirely satisfactory as an adhesion layer in packaging interconnect metallization. Although the use of TiW to sandwich the TiWN is one solution to the adhesion problem, it would be advantageous and more cost effective to provide a packaging interconnect metallization scheme having good adhesion and barrier properties with fewer metallization layers.
Other applications for TiWN have been discussed. In a paper entitled, "Reliability of High Temperature I.sup.2 L Integrated Circuits," by Dening et al, published in IEEE/IRPS Proc. 1984, International Reliability Physics Symposium, pp. 30-36, the use of TiWN as a barrier layer in chip interconnect metallization is discussed. Here it was found that TiWN did not adhere well to the wafer oxide or the gold layer. Sheldon C. P. Lim discusses the use of TiWN as a fuse link and as a barrier metal in U.S. Pat. No. 4,491,860, issued on Jan. 1, 1985. However there is no suggestion that TiWN can be used as an adhesion layer in a packaging interconnect metallization scheme.
The present invention provides for an improved packaging interconnect metallization scheme using TiWN to provide excellent adhesion properties, as well as barrier properties. that is able to withstand high temperatures.
Accordingly, it is an object of the present invention to provide a packaging interconnect metallization scheme having excellent adhesion properties.
Another object of the present invention is to provide a packaging interconnect metallization scheme having excellent barrier properties.
A further object of the present invention is to provide a packaging interconnect metallization scheme having a high resistance to corrosion and exhibiting excellent adhesion properties after being subjected to high temperatures, thus improving the reliability of a semiconductor device.
Yet another object of the present invention is to provide a packaging interconnect metallization scheme having low contact and sheet resistance.
Yet a further object of the present invention is to provide a packaging interconnect metallization scheme using TiWN as an adhesion layer, thus providing lower processing costs.